With two states passing legislation to legalize the commercial production and sale of cannabis, cannabis is becoming more available. Coupled with the recent trend of individuals initiating use at a younger age, and evidence indicating that fewer adolescents consider cannabis use to be associated with significant health risk, further research on its potential impact on psychological health is needed to inform public health policy. Cannabis use has been associated with various psychosis outcomes, including clinical psychotic disorders, the clinical high risk (CHR) period of psychosis, and with sub threshold measures of psychotic symptoms in non- clinical samples, such as attenuated positive psychotic symptoms (APPS). Despite these associations between cannabis use and psychosis, it remains unclear why some individuals who use cannabis are at increased risk for psychosis and why others are not. The present study proposes to examine what individual and contextual- level factors contribute to cannabis use among individuals who are experiencing APPS and/or at CHR for psychosis. The proposed study is the first investigation to use a multi-method design to 1) elucidate the role of peer influences on cannabis use among young adults, and 2) determine individual characteristics that contribute to cannabis use among those endorsing APPS and/or at CHR for psychosis. These individual characteristics include social functioning, mood/anxiety symptoms, motivations and expectancies of cannabis use, negative symptoms, and social context of cannabis use. Such information will provide improved understanding of who, among cannabis users, is most at risk for psychosis, by characterizing profiles of use among those experiencing APPS and those at CHR for psychosis. Further, the proposed study will examine constructs that have been collected in a larger, ongoing protocol that have also been associated with the development of psychosis (e.g., ethnicity, trauma history) using recursive partitioning. The basis of this exploratory approach is to delineate multiple, potentially non-overlapping pathways to cannabis use. The present study will take a dimensional approach to psychotic symptoms as well as examine individuals identified as CHR for psychosis, and will integrate methods from substance use research with methods from investigations of the greater psychosis phenotype. The measurement of APPS in non-clinical samples is crucial, particularly as increases in APPS are associated with increased risk of developing a psychotic disorder, and have a clear dose-response relation with cannabis use frequency. The sample of the proposed study will be 1,000 young adults. Sensitivity to peer influence will be measured experimentally while the remaining variables will be measured via self-report, as well as semi-structured interviews to determine who may be at CHR for psychosis. Findings from this study may 1) identify risk factors for psychosis, 2) delineate pathways to cannabis use in young adults, 3) inform treatment for reducing cannabis use in at-risk populations, and 4) improve our ability to detect which cannabis users may be at increased risk for psychosis.